a) Field of the Invention
This invention relates to a wet multiplate clutch, which is useful primarily in a transmission for an automotive vehicle.
b) Description of the Related Art
FIG. 4 shows the basic construction of a wet multiplate clutch in cross-section. The wet multiplate clutch generally designated at numeral 1 is provided with a clutch case 2 and a hub 3, which are rotatable relative to each other. Plural separator plates 11 and plural friction plates 5 are spline-fitted on the clutch case 2 and the hub 3, respectively, such that the separator plates 11 and friction plates are movable in an axial direction. In the conventional example illustrated in FIG. 4, the separator plate 11 and the friction plates 5 are alternately arranged one by one.
Via the clutch 1, power is transmitted between the clutch case 2 and the hub 3. FIG. 4 also shows a spline groove 21 of the clutch case 2, a spline groove 31 of the hub 3, a piston 6, and a return spring 6 for the piston 6.
When transmission of power is desired, an application of pressure to a right side of the piston 6 as viewed in the drawing causes the piston 6 to move leftwards against the spring 7 so that the friction plates 5 and the separator plates 11 are brought into contact under pressure to transmit the power from the clutch case 2 to the hub 3. Designated at numeral 22 is a snap spring for supporting pressures from the piston. Release of the pressure on the right side of the piston 6 allows the piston 6 to return rightwards owing to the arrangement of the return spring 7, and the clutch is disengaged. In the drawing, an alternate long and short dash line X—X indicates a central axis.
When the separator plates 11 are caused to slidingly rotate relative to the friction plates 5, heat is produced. The wet multiplate clutch of the conventional construction, however, does not permit good transfer of the heat, resulting in development of thermal deformation called “heat spots” on the separator plates 11. FIG. 5 illustrates conditions of the separator plates 11 of the conventional wet multiplate clutch after a test. As shown in this drawing, heat spots 11H have been formed on the surfaces of the separator plates 11. Incidentally, sign 11A indicates spline tabs which are maintained in engagement with the corresponding spline grooves of the clutch case 2.